Patent Literature 1 describes a cell stack in which a cell frame including a bipolar plate, a positive electrode, a membrane, a negative electrode, and a cell frame are repeatedly stacked, and the stack body is sandwiched between supply/drainage plates; and a redox flow battery including the cell stack. The cell frames include a bipolar plate and a frame body disposed on the outer periphery of the bipolar plate. In this configuration, a single cell is formed between the bipolar plates of adjacent cell frames.